A302661 - OEIS

%I #24 Apr 24 2018 02:11:27

%S 1,1,0,-20,-221,-1560,0,272000,6356025,84086080,0,-40560998400,

%T -1449723503125,-28152429760000,0,26582971351040000,

%U 1279483892211136625,32774236110420480000,0,-51128938217766256640000,-3094745459011904478178125,-98456230888859903488000000,0,229377281607595274010624000000

%N Real part of Product_{k=1..n} (k+(n-k+1)i), with i=sqrt(-1).

%C a(n) = 0 for n mod 4 = 2 (A016825). - _Michel Marcus_, Apr 11 2018

%H Seiichi Manyama, <a href="/A302661/b302661.txt">Table of n, a(n) for n = 0..398</a>

%p seq(Re(mul(k+(n-k+1)*I,k=1..n)),n=0..30); # _Muniru A Asiru_, Apr 11 2018

%o (PARI) {a(n) = real(prod(k=1, n, k+(n-k+1)*I))}

%Y Cf. A016825, A301616.

%Y Imaginary part: A302662.

%K sign

%O 0,4

%A _Seiichi Manyama_, Apr 11 2018